Improving the performance of photovoltaic cells based on nanocomposites with contorted polycyclic aromatic hydrocarbon additive in bulk heterojunction

Abstract

Recently, research on the use of additives in photoactive layers to improve the efficiency of solar cells has continued to be conducted. Among them, carbon-based additives serve to increase a device's efficiency by simply and effectively improving the carrier movement. In this work, inverted polymer solar cells (iPSCs) are fabricated based on a blend of PTB7-Th:PC₇₁BM and PTB7:PC₇₁BM bulk heterojunction as photoactive materials using mixed additives of 4Cl-carbon-based contorted hexabenzocoronene (4Cl-cHBC). The 4Cl-cHBC additives, a kind of contorted polycyclic aromatic hydrocarbon, added to bulk heterojunction in the iPSC devices, provide a cocrystal modifier and effective charge separation to enhance device performance. The reason for this efficiency improvement is that cocrystal is formed due to a combination between 4Cl-cHBC and the PTB7-Th:PC₇₁BM bulk heterojunction, which reduces bimolecular recombination in the device and significantly increases short-circuit current and fill factor. The R_S and R_Sh values of iPSCs based on PTB7-Th:PC₇₁BM with and without the 4Cl-cHBC additives decreased from 7.0 Ω cm² to 4.0 Ω cm², and increased from 813 Ω cm² to 1226 Ω cm², respectively. The calculated average carrier lifetimes at 500 nm for PTB7-Th:PC₇₁BM and PTB7-Th:PC₇₁BM with 4Cl-cHBC additives are 4.46 ps and 3.06 ps, respectively. The carrier lifetimes show that the charge separation of PTB7-Th:PC₇₁BM with 4Cl-cHBC additives is more than 45% faster. As a result, the iPSCs based on the blend of PTB7-Th:PC₇₁BM and PTB7:PC₇₁BM with 4Cl-cHBC additives showed maximum power conversion efficiencies of 9.46 and 8.62%, which were 20.6 and 19.95% higher than those of the reference, respectively.